I keep this Mace night Defender at the front door on a shelf. It's a gel pepper spray and if someone knocks on the door I usually grab it and answer ready to spray them. It should give me enough time to get to my real weapons.

If she's hellbent in pepper spray, buy her a small knife she can keep on her key chain too. Often times, especially with doped up muggers, the pepper spray will stun and disorient but they'll still be able to come at you. Make sure she has a second line if defense if she relies on pepper spray.